Many problems or abnormalities with body functions can be caused by damage, disease, disorders, and/or developmental difficulties in the brain. For example, strokes are generally caused by emboli (e.g., obstruction of a vessel), hemorrhages (e.g., rupture of a vessel), or thrombi (e.g., clotting) in the vascular system of a specific region of the brain. These events generally cause a loss or impairment of neural function. Other abnormalities are caused by chemical imbalances that affect specific regions of the brain.
A wide variety of mental and/or physical processes are controlled or influenced by neural activity in particular regions of the brain. Several mental and/or physical processes generally correspond or “map” to one or more relatively discrete neural populations within the brain such that the brain exhibits a functional organization according to the cognitive and/or physical processes controlled by the relatively discrete neural populations. The particular regions of the brain that control given types of functions are also generally consistent from one group of individuals to another. In the majority of people, for example, the regions of the left interior frontal lobes relate to language. As another example, particular regions of the cerebral cortex appear to be consistently involved with conscious awareness, memory, and intellect. As shown in FIGS. 1A and 1B, the neural regions associated with the human vision system include the optic nerve, the optic chiasm, the optic tract, the lateral geniculate nucleus, the optic radiation, and the occipital lobes (i.e., the visual cortex/center).
Neurological disorders, disease, and/or damage may impair neural activity within one or more neural populations. This typically results in deterioration and/or loss of physical and/or cognitive abilities associated with the affected neural populations. Thus, as a result of neurological disease or damage, one or more neural populations and/or portions of an individual's neurofunctional map may become impaired, dysfunctional, or essentially nonfunctional. Damage, disease, and/or disorders in the brain resulting from, for example, stroke, traumatic brain injury, or other causes may give rise to various types of visual disorders. Such visual disorders may result in partial blindness or visual field defects such as tunnel vision, hemianopia, quadrantanopia, and/or scotoma.
Effectively treating neurological abnormalities has traditionally been very difficult. For example, physical therapy treatments for stroke patients either alone or in combination with drug treatments fail to significantly improve the function of an affected body part beyond the generally limited recovery that occurs naturally without intervention. As a result, many types of physical and/or cognitive deficits that remain after treating neurological damage or disorders are typically considered permanent conditions that patients must manage for the remainder of their lives.
As an individual acquires a new physical capability, a new memory, or learns or perfects an ability or skill, the extent to which this capability, memory, or skill is functionally represented or implemented by neural connections within particular regions of the brain strengthens or increases. For example, as a guitar player becomes increasingly proficient over time, the number and/or strength of neural connections within the motor cortex directed toward controlling fine finger movements increases. The ability of the brain to structurally adapt in a manner that facilitates neurofunctional map organization, expansion, and/or reorganization is referred to as neuroplasticity.
For patients having certain types of visual field deficits, specific types of vision training may stabilize, improve or enhance visual function. Such stabilization or improvement may result from neuroplastic change or reorganization in vision-related neural populations. U.S. Pat. No. 6,464,356 (see also www.novavision.info), which is incorporated herein by reference, describes a system and technique for improving visual function through selective application of optical stimuli to a patient's visual system. The system and methods described in U.S. Pat. No. 6,464,356 may increase the likelihood of influencing or affecting neurons capable of undergoing neuroplastic change.
Neural activity in the brain can also be affected by electrical or magnetic energy supplied from a waveform generator or other type of device. Various patient perceptions and/or neural functions may be promoted or disrupted by delivering an electrical or magnetic stimulation signal to the brain. A need exists for a neural stimulation system and method that is capable of enhancing or maximizing a likelihood of developing, stabilizing, restoring, and/or rehabilitating visual function on a long term or permanent basis.